The present invention relates to a facsimile apparatus in which an analog/digital converter, used for converting analog image signals to digital image signals, can be shared with other analog sensors so as to convert analog signals from other sensors into digital signals.
In a conventional facsimile apparatus, a high speed and high resolution (having a large number of bits) analog/digital (A/D) converter is provided for converting analog image signals, obtained by a scanner scanning an original, into digital image signals.
The conventional facsimile apparatus also has various sensors, such as a temperature sensor, for outputting analog signals. In order to read detection signals from the analog sensors by a microcomputer system provided in the facsimile machine, it is required that these analog signals be converted into digital signals. Accordingly, in the conventional facsimile apparatus, an A/D converter is provided for each analog sensor. Such a construction results in a large number of A/D converter being provided in one facsimile apparatus, and thus manufacturing costs of the facsimile apparatus are increased.
In order to eliminate the above-mentioned problem, Japanese Laid-Open Patent Application No. 4-47751 (titled "facsimile apparatus") has proposed an improved facsimile apparatus. In this improved facsimile apparatus, a plurality of analog signals, including analog image signals and various analog sensor signals, are converted into corresponding digital signals by a single A/D converter with a multiplexer used for sequentially switching analog signal inputs from the sensors.
However, in the above-mentioned facsimile apparatus, there are the following problems:
a) to perform a scanning operation, a signal for operating the multiplexer must be generated; PA1 b) the accuracy of the digital signals output from the A/D converter may be deteriorated if an amplitude of voltage of the analog sensors differs from sensor to sensor; PA1 c) because an A/D converter for converting analog image signals into digital signals is used, the digital signals output from the A/D converter have an unnecessarily large number of bits, and thus the analog sensors occupy a large memory area; PA1 d) although signals from different analog sensors are sampled during the same period, it is not always required that the sampling frequency for each analog sensor be the same; and PA1 e) because the digital signals converted by the A/D converter are stored in a memory of an upper controlling circuit, an address control of the analog to digital conversion system may become complex. PA1 a multiplexer provided for selecting one of analog signals including the analog image signal and the analog detection signal; PA1 an analog/digital converter converting the one of the analog signals selected by the multiplexer into a digital signal; PA1 a primary scanning counter counting the number of pulses of a pixel clock signal indicating a reading timing of each pixel so as to output a first count value, the first count value being reset each time a line synchronization signal indicating a first position of each scanning line is supplied thereto; and PA1 a decoder provided for generating a first selection signal in accordance with the first count value supplied by the primary scanning counter, and supplies the first selection signal to the multiplexer so that the multiplexer selects one of the analog signals corresponding to the first selection signal. PA1 a multiplexer provided for selecting one of the analog signals including the analog image signal, the first analog signal and the second analog signal; PA1 an analog/digital converter converting the one of analog signals selected by the multiplexer into a digital signal; PA1 a primary scanning counter counting the number of pulses of a pixel clock signal indicating a reading timing of each pixel so as to output a first count value, the first count value being reset each time a line synchronization signal indicating a first position of each scanning line is supplied thereto; and PA1 a decoder provided for generating a first selection signal in accordance with the first count value supplied by the primary scanning counter, and supplying the first selection signal to the multiplexer so that the multiplexer selects one of the first analog signals corresponding to the first selection signal, PA1 the first selection signal being generated, when a signal representing a detection timing of the second analog signal output from the second sensor is supplied to the decoder means, so that the second analog signal output from the second sensor is selected by the multiplexer.